1. Field of the Invention
The present invention relates to a broadband antenna, and more particularly to a broadband antenna applied to multiple frequency band.
2. Description of Related Art
With the development of wireless communication technologies, wireless transmission technologies are widely used in mobile information media or personal data management tools. For example, electronic products, such as notebook computers and so on, usually need to transmit/receive data to/from other data devices. Based on wireless transmission technologies, many structures can be simplifies and many connecting wires can be avoided.
To achieve the above-mentioned wireless transmission, conventional electronic products must have antennae, and most of the electronic products have inbuilt antenna devices for wireless communication. Antennae of conventional electronic products are generally divided into two categories as planar and inverse F-shaped panel antennae and monopole antennae. With the miniaturization development of electronic products, antennae need to be smaller and smaller. However, because frequency bandwidth, gain values and radiation efficiencies of planar and inverse F-shaped panel antennae are proportional to the volume of the antennae, the planar and miniaturized design for antennae causes that their frequency bandwidth and radiation efficiencies are reduced greatly. So broadband antenna devices formed by planar and inverse F-shaped panel antennae usually have narrow frequency bands, which cannot covers the 5.2˜5.8 GHz work frequency range under IEEE802.11a and the 2.4˜2.5 GHz work frequency range under IEEE802.11b simultaneously. Though monopole antennae have wide frequency bands, they must have large ground portions during use, which limits limited using space of electronic products such as notebook computers.
In other words, though there have been antenna devices which can work in dual frequency bands, relationships between elements of the antenna devices must be considered when operation frequency bands of the antenna devices are adjusted, which causes that the antenna devices have complicated structures. Furthermore, with the miniaturization development of wireless electronic products, antennae must be limited in a certain volume to meet the requirements of the electronic products. Accordingly, how to design smaller, lighter and stable antennae is a problem desired to be solved in wireless technology fields.